Mostly I like it honestly. I'm not a big fan of the brother/sister dynamic, but I know what I signed up for and the fact is, most things around here feature some sort of incest. And even if you can replace it, it's usually terrible implemented. "Oh no, I can't have feelings for my ROOMMATE, it's illegal." No it fucking isn't. But this isn't what I wanted to talk about.
What I actually wanted to talk is that this gives me a vibe that dev doesn't have siblings. Nobody calls their sister "sister" or brother "brother." They're called by their given names. Occasionally you call them a cunt, dude, idiot. But I can't remember EVER calling my siblings "Hey sister/brother." Or heard anyone do that. I introduce them as my siblings, sure. I know it plays into the very genre or fetish or whatever but there has to be a way to make it feel more natural.
Beyond that I like it. It delivers exactly what it promises. It's not overcomplicated, neither does it pretend to be something it's not. Everything is at least acceptable quality and I believe it will keep going upwards as the dev gains even more experience. In overall, fine job.